Field of the Invention
The present invention relates to a self-supporting overhead telecommunication/power cable.
Description of the Related Art
Self-supporting overhead telecommunication/power cables are widely used for aerial or suspension installation comprising a cable suspended in catenary from poles or surrounding buildings. Such cables can include both optical fibre conductors and electrical conductors so as to combine in the same cable the high bit-rate capacity of optical fibre conductors with the electric signal/power carrying capacity of electrical conductors, thus achieving operational and installation benefits for the users.
Among the known self-supporting overhead telecommunication/power cables, the so called figure-8 cables are highly appreciated for allowing cost effective aerial installations. These cables comprise a supporting portion and a transmission portion mutually operatively connected according to a figure-8 configuration. The supporting portion includes a messenger wire intended to be attached to poles during installation, while the transmission portion includes both the optical fibre conductors and the electrical conductors.
The Applicant observed that in installation and operation, the self-supporting overhead telecommunication cables can suffer stresses due to possible external loads. These external loads may be caused, for example, by environmental phenomena, such as ice and/or wind.
Strength and/or protective members should be properly arranged within the cable so as to provide a desired structural strength against the abovementioned external loads and to avoid overloads and strains on the conductors, especially the optical fibre conductors, otherwise the transmission quality might be affected and the optical fibre conductors might break.
“Loose Tube Figure 8—Installation in aerial, up to 80 m span” brochure (Prysmian Group, 2012), relates to a figure-8 optical cable with a central strength member and a plurality of loose tubes SZ stranded around the central strength member and containing optical fibres. Peripheral strength elements are envisaged.
U.S. Pat. No. 5,095,176 relates to a figure-8 aerial cable including a transmission portion and a supporting portion. The transmission portion includes a core having a plurality of transmission media. The transmission media may include a plurality of insulated metallic conductors or a plurality of optical fibers. The core is enclosed in a sheath system. A first component of the sheath system is a metallic shielding layer wrapped around the core. Surrounding the shielding layer is an outer second metallic shield which provides mechanical protection to the cable.
U.S. Pat. No. 6,861,590 relates to a figure-8 cable comprising a load bearing portion and a communication conveying portion. The communication conveying portion includes optical fibers and/or electrical wires. A reinforcing member is provided in the communication conveying portion. The optical fibres are arranged around the reinforcing member. To protect the optical fibers, a relatively soft layer, such as yarn or jell, is provided around the optical fibers and a tape is wrapped around the yarn layer.
U.S. Pat. No. 5,777,260 relates to a coaxial cable having an inner conductor and an outer conductor. An intermediate layer is arranged on the outer conductor. The intermediate layer has depressions in which at least one light waveguide is arranged, the depressions running helically around the cable axis. Reinforcing elements and/or supporting elements can be introduced in the intermediate layer for enhancing the tensile strength. In an embodiment, an 8-shaped cable is provided, wherein two inside spaces are formed. The hybrid cable is accommodated in the larger inside space while in the smaller inside space light waveguides or other transmission elements can be subsequently introduced. The 8-shaped cable can be secured to a carrier cable with continuous clips, so that an aerial cable arises.
U.S. Pat. No. 5,917,977 relates to a composite cable including a core section, a tensile strength section, a conductor and water blocking section, an armor tape and outer jacket. The core section includes a fiber optic conductor disposed inside a buffer tube. The tensile strength section includes strength members, for example impregnated fiberglass members with a helical lay about the buffer tube. The conductor and water blocking section includes twisted pairs conductors stranded about the strength member. The conductor and water blocking section may also include one or more fiber optic conductors. The armor tape comprises for example a steel tape material and provides electrical shielding and protection against rodents. A low-cost easily manufacturable composite cable may be formed without the strength member.